LRP5- linked osteoporosis-pseudoglioma syndrome mimicking isolated microphthalmia

Optic cup morphogenesis across species and related inborn human eye defects

The vertebrate eye is shaped as a cup, a conformation that optimizes vision and is acquired early in development through a process known as optic cup morphogenesis. Imaging living, transparent teleost embryos and mammalian stem cell-derived organoids has provided insights into the rearrangements that eye progenitors undergo to adopt such a shape. Molecular and pharmacological interference with these rearrangements has further identified the underlying molecular machineries and the physical forces involved in this morphogenetic process. In this Review, we summarize the resulting scenarios and proposed models that include common and species-specific events. We further discuss how these studies and those in environmentally adapted blind species may shed light on human inborn eye malformations that result from failures in optic cup morphogenesis, including microphthalmia, anophthalmia and coloboma.

Effects of Stress on Osteoblast Proliferation and Differentiation Based on Endoplasmic Reticulum Stress and Wntβ-Catenin Signaling Pathway

In order to investigate the effect of fluid shear stress on the proliferation of osteoblasts and the regulatory role of the Wnt/β-catenin signaling pathway in cell proliferation, a new method based on endoplasmic reticulum stress and Wnt/β-catenin signaling pathway stress-mediated was proposed. Taking MG63 osteoblasts as the research object, they were inoculated on glass slides (G group), polished titanium sheets (P group), and sandblasted acid-base treated pure titanium sheets (S group). In addition, FSS of 0 dunes/cm2 (static group) and 12 dunes/cm2 (stress group) were given, respectively. Then, quantitative reverse transcription-PCR (RT-qPCR) and western blot were used to detect the mRNA and protein expressions of low-density lipoprotein receptor-related protein 5 (LRP5) and β-catenin in MG63 cells. The results showed that the expression levels of β-catenin mRNA and protein in cells in the stress group were significantly increased (P < 0.05), and the protein expression level of LRP5 was significantly decreased (P < 0.05). The expression level of LRP5 in group S was greatly inhibited, while the expression level of β-catenin was significantly upregulated. Therefore, FSS can stimulate the expression of LRP5 and β-catenin in osteoblasts. Fluid shear stress can promote osteoblast proliferation in vitro; the Wnt/β-catenin signaling pathway is involved in regulating fluid shear stress to promote osteoblast proliferation.

Exome sequencing identifies genetic variants in anophthalmia and microphthalmia

Anophthalmia and microphthalmia (A/M) are rare birth defects affecting up to 2 per 10,000 live births. These conditions are manifested by the absence of an eye or reduced eye volumes within the orbit leading to vision loss. Although clinical case series suggest a strong genetic component in A/M, few systematic investigations have been conducted on potential genetic contributions owing to low population prevalence. To overcome this challenge, we utilized DNA samples and data collected as part of the National Birth Defects Prevention Study (NBDPS). The NBDPS employed multi-center ascertainment of infants affected by A/M. We performed exome sequencing on 67 family trios and identified numerous genes affected by rare deleterious nonsense and missense variants in this cohort, including de novo variants. We identified 9 nonsense changes and 86 missense variants that are absent from the reference human population (Genome Aggregation Database), and we suggest that these are high priority candidate genes for A/M. We also performed literature curation, single cell transcriptome comparisons, and molecular pathway analysis on the candidate genes and performed protein structure modeling to determine the potential pathogenic variant consequences on PAX6 in this disease.

Osteoporosis-pseudoglioma syndrome in four new patients: identification of two novel LRP5 variants and insights on patients' management using bisphosphonates therapy

This study describes the clinical, radiological, and molecular data of four new patients with osteoporosis-pseudoglioma syndrome and assesses their response to bisphosphonate therapy.

INTRODUCTION

Osteoporosis-pseudoglioma syndrome (OPPG) is a very rare disorder characterized mainly by severe juvenile osteoporosis and congenital blindness. OPPG is caused by biallelic mutations in the gene encoding low-density lipoprotein receptor-related protein 5 (LRP5).

METHODS

We present the clinical, radiological, and molecular findings of four new patients with OPPG from Egypt. We also assessed patients' response to oral and intravenous bisphosphonate therapy.

RESULTS

All patients had reduced bone mineral density (BMD) with variable number of fractures per year, in addition to bone abnormalities and the characteristic eye phenotype associated with OPPG. Mutation analyses of LRP5 gene revealed three different homozygous variants including two novel ones, c.7delG (p.A3Qfs*80) and c.3280G > A (p.E1094K). The c.3280G > A (p.E1094K) was recurrent in two unrelated patients who shared a unique haplotype suggesting a possible founder effect. The use of bisphosphonate therapy was beneficial; however, intravenous bisphosphonate administration led to a more favorable response.

CONCLUSION

Our study described the phenotypic and genetic features of four patients with OPPG and identified two new LRP5 variants, thus expanding the mutational spectrum of OPPG. In addition, our study reinforces the efficiency of using intravenous bisphosphonates in the management of patients with OPPG.

Inherited eye diseases in Turkey: Current approaches and future directions

The aim of this review is to reveal Turkey's current status of medical practice in inherited eye diseases and the necessary steps to improve healthcare services and research activities in this area. Since consanguinity rate is high, disease burden is estimated to be high in Turkey. Universal health insurance system, easily accessible medical specialists, increasing genetic test, and counseling opportunities are the key advantages of Turkey's healthcare system. However, specialized clinics for inherited eye diseases, low-vision rehabilitation services, training of ophthalmologists about the recent developments in ocular genetics, and multidisciplinary translational research are the main headlines needed to be focused for better health services and successful research in Turkey.

Luteolin attenuates glucocorticoid-induced osteoporosis by regulating ERK/Lrp-5/GSK-3β signaling pathway in vivo and in vitro

Glucocorticoid-induced osteoporosis (GIO) is a secondary osteoporosis with extensive use of glucocorticoids (GCs). GCs can increase bone fragility and fracture via inhibiting osteoblastic proliferation and differentiation. Luteolin (LUT), a kind of plant flavonoid, has been reported to exhibit the antioxidant activity, but the effects of LUT on GIO still remain unclear. This study aimed to investigate the effects of LUT on GIO both in vivo and in vitro and elaborate the potential molecular mechanisms. LUT increased the superoxide dismutase activity, glutathione level and decreased reactive oxygen species (ROS) level and lactate dehydrogenase release in GIO. Meanwhile, LUT decreased caspase-3, caspase-9, and Bax protein expressions and increased Bcl-2 protein expression in GIO. LUT increased the ratio of osteoprotegerin (OPG)/receptor activator of nuclear factor-κB Ligand (RANKL) messenger RNA (mRNA) expression and mRNA expression levels of osteogenic markers, including runt-related transcription factor 2, osterix, collagen type I, and osteocalcin. LUT also enhanced the extracellular signal-regulated kinases (ERK) phosphorylation, glycogen synthase kinase 3β (GSK-3β) phosphorylation, mRNA expression levels of lipoprotein-receptor-related protein 5 (Lrp-5) and β-catenin. Further study revealed that Lrp-5 small interfering RNA (siRNA )and ERK-siRNA reduced the effects of LUT on GSK-3β phosphorylation, alkaline phosphatase (ALP) activity and the ratio of OPG/RANKL mRNA expression. Moreover, ERK-siRNA decreased Lrp-5 mRNA expression in vitro. These results indicated that LUT promoted proliferation by attenuating oxidative stress and promoted osteoblastic differentiation by regulating the ERK/Lrp-5/GSK-3β pathway in GIO. This study may bring to light the possible mechanisms involved in the action of LUT in GIO treatment, and benefit for further research on GIO.

Novel Homozygous LRP5 Mutations in Mexican Patients with Osteoporosis-Pseudoglioma Syndrome

AIMS

Osteoporosis-pseudoglioma syndrome (OPPG) is an uncommon autosomal recessive disorder characterized by the rare association of early-onset osteoporosis and severe ocular abnormalities such as persistent fetal vasculature and microphthalmia. Biallelic mutations in the low-density lipoprotein receptor-related protein-5 gene (LRP5) have been associated with OPPG. We present clinical and genetic data from three Mexican OPPG patients, a pair of sibs, and a sporadic case.

MATERIALS AND METHODS

Three patients underwent clinical examination, including a complete ophthalmic evaluation. Based on the clinical diagnosis of OPPG, the entire coding sequence of LRP5 was polymerase chain reaction-amplified and directly Sanger-sequenced. Genetic testing was extended to the parents of the affected patients.

RESULTS

Phenotypic variability was observed in the familial case and molecular analysis identified a novel homozygous c.1145C>T, p.(Pro382Leu) variant in both sibs. As expected, their parents were heterozygous carriers. The sporadic patient exhibited a severe osseous phenotype, microphthalmia, and neurological symptoms. In this patient, homozygosity for the c.442C>T, p.(Gln148*) variant was demonstrated, whereas her parents were heterozygous carriers. The p.(Pro382Leu) pathogenic mutation has been previously reported only in a compound heterozygous state in OPPG patients.

CONCLUSIONS

Two novel homozygous missense and nonsense variants were demonstrated in three OPPG cases from Mexico. Our results expand the spectrum of disease-causing LRP5 mutations. This is the first report of OPPG in our population and our findings may potentially add to a genotype-phenotype correlation.